The nature of visual transduction will be examined by studying both visual pigments and model compounds which mimic visual pigment chromophores. The visual pigments can provide direct kinetic evidence for changes which occur upon exposure to light. This photochemical process is quite complex and our understanding of it will be aided by investigating simpler model compounds, namely polyenes, whose photochemistry is simpler. Model compound studies will include two-photon spectroscopy and excited state spectroscopy of small polyenes, diphenylpolyenes, and retinyl polyenes. These techniques will tell us the state ordering of these molecules and thus provide information about their photochemistry. Visual pigment studies will involve flash photolysis studies on nanosecond, microsecond, and millisecond time scales. We will study the kinetics of the bathorhodopsin to lumirhodopsin, lumirhodopsin to metarhodopsin I, and metarhodopsin I to metarhodopsin II transitions. Detailed investigations of the kinetics of these reactions under a variety of conditions should yield valuable information on the nature of the visual transduction process.